A casing including a cover (lid) to be opened and closed about a rotation shaft such as a retractable cover made of a resin is generally provided with a ready-made push latch as disclosed in Patent Document 1, and opens and closes the cover by a push action. A holding section is provided for the cover of the push latch attached to the casing, and a convex striker adapted to a concave shape of the holding section is provided for the other cover. In such a casing, as the cover in an opened position is pushed to a locking point while forcing the striker into the holding section, the push latch is in a locked position, and the cover is in a closed position by the engagement between the striker and the holding section. When the cover in the closed position is pushed, and the holding section together with the striker is pushed to a lock-releasing point, the push latch is lock released, and the holding section is tilted while being thrust back to be disengaged from the striker. Then, the cover is opened.